Various properties are required for lubricants to be utilized for internal combustion engines. It has become common knowledge to add one or more chemical additives to a lubricant in order to improve engine properties. Depending upon the required properties, various additives such as detergents/dispersants, antioxidants, antifoam agents, viscosity-index improvers, corrosion inhibitors, rust inhibitors and the like have been utilized. Among them, detergents/dispersants are generally added to various lubricants to be used for internal combustion engines and are particularly important.
In recent years, internal combustion engines have been operated continuously for a longer span of time at higher temperatures due to the improvements in structures and materials of engines. This has created a demand for engine oils which may withstand continuous use for a longer span of time at higher temperatures. Improvements of engine oils in various properties, even though they are small in numerical values, have great significance from a practical view point.
Various properties of engine oils are derived from chemical structures of the additives and functional groups contained therein. Different chemical structures may give different properties or characteristics and the increase in kind and number of functional groups included may give different activities. Also it is true that, in proportion, as functional groups in a molecule of an additive compound increase in kind and number, the activities are greatly extended and the effects increase.